Hydraulic load limiting system

ABSTRACT

Apparatus for limiting the load on a hydraulic drive system, such as a winch. A feature of the disclosed arrangement is that limiting is maintained at a relatively constant value regardless of whether the load is being controlled by the hydraulic drive or is overpowering the drive.

United States Patent Bentkowsky et al.

[ 1 June 6,1972

[54] HYDRAULIC LOAD LIMITING SYSTEM [72] Inventors: Jerome Bentkowsky, Los Altos; W. Tait Beran, Palo Alto, both of Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy [22] Filed: Mar. 5, 1971 [21] Appl. No.: 121,330

[52] US. Cl. ..60/53 WW, 60/53 R, 91/444 [51] im. Cl ..Fl6d 31/06 581 Field of Search ..eo/53 ww, 53 R; 91/444 [56] References Cited UNITED STATES PATENTS 2,104,780 1/1938 Vickers ..60/53 WW UX Smith ..60/53 WW Huf ..60/53 WW X Primary Examiner-Edgar W. Geoghegan AttorneyRichard S. Sciascia, Q. Baxter Warner and Howard J, Murray, Jr.

[ ABSTRACT Apparatus for limiting the load on a hydraulic drive system, such as a winch. A feature of the disclosed arrangement is that limiting is maintained at a relatively constant value regardless of whether the load is being controlled by the hydraulic drive or is overpowering the drive.

7 Claims, 2 Drawing Figures HAUL-IN PATENTED 6 1973 N ol PDO Q 27 1 31 (\1 JEROME BENTKOWSKY W TAIT BERAN INVENTORS 3W%.M Q6 GENT Q/ ATi R EY HYDRAULIC LOAD LIMITING SYSTEM STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION It is customary in the design of hydraulic drive trains to provide for at least some degree of overload protection. This may take the form of means for sensing and controlling the upper limit of hydraulic pressure, for example, or it may embrace the use of slip clutches and/or relief valves. Such expedients not only add to the complexity of the equipment, but in addition fail to take into account difierencesbetween the respective forward and back driving mechanical efficiencies of any bidirectional power transfer system.

SUMMARY OF THE INVENTION The present concept overcomes the disadvantages of known arrangements by incorporating therein means for reducing the variation between maximum driving tension and maximum driven tension, particularly in high speed ratio drive trains. This is achieved by recognizing and compensating for differences in the system when driving a load compared to being backdriven by a load.

STATEMENT OF THE OBJECT OF THE INVENTION One object of the invention, therefore, is to provide an improved form of overload protection for hydraulic drive trains.

Another object of the invention is to provide a hydraulic control system for winches in which tension limiting is maintained at a relatively constant value during both haul-in and pay-out operation, whether or not the load backdrives the winch.

A further object of the invention is to accomplish such loadlimiting without utilizing either slip clutches or external hydraulic control systems.

Other objects, advantagesand novel'features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of a preferred form of hydraulic load-limiting system embodying the principles of the present invention; and

FIG. 2 is a schematic diagram of a modified form of loadlimiting system in which there is no minimum supply pressure limitation.

DESCRIPTION OF THE PREFERRED EMBODIMENT One environment in which the present concept is particularly useful is for either haul in or haul-down winch conn'ol on an undersea research vehicle, where inertia and buoyancy effects can combine to produce large overrunning transient cable tensions. Although obviously not limited to such an application, the principles of the invention will be set forth hereinafter in conjunction with such an arrangement.

A load supported by a cable 12 is schematically illustrated in FIG. 1 of the drawings. Cable 12 is wound on a winch drum 14, the winch being driven by a fixed-displacement hydraulic motor MF through a gear reducer such as a harmonic drive (schematically designated by the reference numeral 16).

Pressurized fluid from a source P (which may be the research vehicles supply at 3,000 psi above return pressure) drives motor MF through a solenoid-ope'ratedvalve V1. When solenoid S] on V1 is energized, pressure is applied to line A to turn the winch drum 14 in the payout direction.

Typically, the efiiciency of hydraulic motor MF and the gear drive 16 is in the order of 50 to 60 percent. Thus, if 3,000 psi across the motor is required in order to achieve rated load on the output of the winch, then, when operated in the reverse direction with the load driving the winch, rated load will result in the application of El x E2 x 3,000 psi, where E1 gear efliciency in driving direction, and

E2 'efiiciency in the driven direction. For purposes of illustration, it can be assumed that E l X E2 0.3 so that, in the driven direction, rated load will result in 900 psi across motor MF.

V2 and V3 are pressure-compensated flow control valves, regulating flow in the direction of the respective arrows. For flow in the opposite directions, V2 and V3 are bypassed by check valves V4 and V5, respectively.

V6 is a piloted relief valve. In the absence of pressure in line C, V6 acts as a relief valve with a setting of P 900 psi. The

pilot area is approximately l0.times the flow area; Thus, V6 opens for relativelysmall values or'pressure in line D. The condition for V6 opening is For relatively large values of P the pressure drop across the valve is very low, while for small values of P the pressure drop will adjust to the flow requirements.

V6 in combination with check valve V7 also acts as an overcenter valve. Flow through V6 is bypassed when P,; is greater than PD.

An important component of the disclosed system is the valve designated as V8 in FIG. 1. This is a hydraulically operated, two-position, six-way valve, with a bias spring in one direction only. In its normal unactuated position (illustrated) V8 permits flow of fluid between the overcenter unit V6-V7 and line F. It also connects line B to pilot connection A, of V8. The condition for V8 moving to the right is P (Ad/1,) P P psi In the example P 805 psi The values of 14 1/1, and the bias pressure are selected to assure operation at some minimum supply pressure, and also to preclude valve chattering under certain load conditions.

With V8 in its actuated state, pilot line A and lines E, C and G are connected together. Through either check valve V9 or V10, line C is connected to the return side of the hydraulic supply. Check valve Vll is provided for pressure compensation and for fluid makeup.

The valve V1 has three settings (a) neutral, (b) payout, and (c) haul-in.

a. Neutral In this position, the pressure to pilot line A is 0. With no flow in the system, the pressure on line C (P is also 0, and the load pressure P P P,,. When P reaches 805 psi, V8 shifts to the right, tying lines A and C together. When P reaches 900 psi, V6 opens, permitting flow through the motor MF, V6 and V8, thereby causing the winch to slip. V6 acts as a relief valve, keeping the load pressure very nearly equal to 900 psi, independent of slipping rate. This arrangement holds output loads below rated, but permits the winch to slip if larger loads are induced.

b. Payout In the pay-out direction, 3,000 psi is applied to line A, and line B is connected to return. In normal operation, return flow is through check valve V5 so that P is very nearly equal to P,,, or return pressure. There is also only return pressure on pilot port A The action of V8 thus depends solely on the pressure on pilot port A,, or P In ordinary payout operation, it is necessary to overcome friction in the system, so that the pressure on line C (P is greater than on line D (P P pilots V6, causing a relatively low pressure drop thereacros s. P will therefore W be small, and V8 will remain in the illustrated position. If an. overrunning load is applied, P will be reduced, constricting V6, and thereby increasing P V8 will shift to the right when P increases to 805 psi, tying lines E and F back to return through check valve V10. When the load pressure P reaches 900 psi, V6 opens andthe winch will slip. It will be noted that line C is tied to return via V11, bypassing flow control valve V2, to prevent cavitation regardless of the overrunning speed of motor MF. Haul-in In the haul-in direction, 3,000 psi is applied to line B, and line A is connected to return. In ordinary operation (load being significantly lower than rated) flow is directed through V7 so that V6 is effectively bypassed. The drop through V7 is very small, so that P,; can be considered equal to P The difierence between load-pressure and supply pressure for a given speed is absorbed by flow control valve V3. With the system parameters as described, if P is less than 2,680 psi, then V8 will remain as illustrated. When P equals or exceeds 2,680 psi, then P (Ag/A P -i- 805 and V8 will shift to the right.

When V8 shifts to the right, pilot line A, is connected to return through V8 and V9, reducing the pressure on A so that V8 will remain shifted until P is reduced below 805 psi. Since P is now 2,680 psi greater than P valve V6 will open. The direction of flow through the motor MF will reverse, and

the motor will slip'until the load pressure drops below 900 psi.

When the load pressure is between 900 psi and 805 psi the winch will stall. When the pressure drops below 805 psi, haulin action will resume. The pressure required to drive the winch will be less than 2,680 psi, and the winch will continue to haul Proper system operation depends upon the selection of the pressure ratios P /P and the area ratio A /A,. If P /P is set too low the system will tend to hold rather than to haul in unless the load pressure is significantly below'the rated value (P,,). If P-,-/P,, is set too high the system will tend to chatter (i.e., system operation oscillating between pay out, hold and haul in) if the haul in load is very nearly equal to P Once P IP has been selected, A /A is selected to assure that the system will operate at the minimum value of supply pressure to be expected. If A lA is set too high, the system will not operate. for reduced supply pressures. If Ag/A is set too low, the system will tend to hold rather than to haul in unless the load pressure is significantly below the rated value. With the parameters selected the system will operate with supply pressures as low as 2,680 psi.

An important feature of the disclosed system is the connection of line C to return when V8 is shifted. Since in the pay-out mode an overload could otherwise cause P to reach 3,900 psi, connecting line C to return limits the pressure without adding any complexity to V8.

' The following is the sequence of valve operations taking place when V8 is moved from left to right: a. The land connecting line G to line A is opened first. This connects line A to return through valves V9 or V10.

b. The land connecting line E is opened.

0. The land connecting pilot line A is connected to line G.

d. The land connecting line B is connected to line G.

Consider the following operational characteristics in each of the three modes;

v a. Neutral in the neutral. mode, slippage is a function only of theaction of V6. As long as V8 operates at any pressure lower than V6, the desired results occur.

b. Pay-out the initial action is the connection of line A to retum. When this occurs, the pilot operation of line A on V6 is cut ofi. The system functions in a manner similar to the neutral mode that is, the winch will hold until the load pressure exceeds 900 psi.

c. Haul-in the connection of line A to return has no effect, since, in this mode, line A is initially essentially at return pressure. As soon as the pilot line is connected to return, the valve will move to the right very rapidly, completing the cycle of operation. As the load pressure decreases, pilot line A: is connected to line B before flow starts through line E. The valve will move to the left very rapidly, opening line F to line E.

A modified load-limiting system is shown in FIG. 2 of the drawings. In this embodiment, the pilot line port connections are eliminated from valve V8, making the latter a four-way valve rather than a six-way valve as set forth in FIG. 1. The new valve is designated as V8 in FIG. 2.

In addition, a three-way, two-position spring-loaded valve V12 is connected across V3 and V5. When P, P l50 psi (approx.), pilot line A, of V8 is connected to B. When I, P, psi (approx.), pilot line A, is connected to return.

The addition of valve V12 in FIG. 2 takes the place of the unequal-area effect of valve V8 in FIG. I, so that A and A, can be equal in the modified system.

It should be noted that there is a setting for V8 such that, with P P 150 psi, and P 850 psi, the orifice connecting line E to line F can be such that the pressure drop P P,- 2,000 psi (approx.). Under these circumstances, V8 rather than V3 acts as the flow control element, limiting the flow rate below the desired level. However, this is unlikely to occur in practical applications of the invention system.

The setting of V12 should be selected at a level sufficiently high to prevent chattering when the load is near rated for example, 150 psi is a satisfactory minimum. However, the

system of FIG. 2 does not have a minimum supply pressure limitation.

Obviously many modifications and variations of the present invention are powible in the light of the above teachings. It is therefore to be understood that within .the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

1. Apparatus for limiting the load on the output of a hydraulic drive system to an essentially constant value regardless of whether the load is being driven or is overpowering the drive, said apparatus comprising:

a source of pressurized fluid;

a fixed displacement hydraulic motor;

a load connected to said motor;

a first control valve having a neutral position and two selectively settable positions;

means responsive to the selective actuation of said first valve to one of its two settable positions to cause fluid to flow from said source through a first conduit to operate said motor in one direction of rotation;

means responsive to the selective actuation of said first valve to the other of its two settable positions to cause fluid to flow from said source through a second conduit to operate said motor in the opposite direction of rotation;

a relief valve in said second conduit; and

a second two-position valve located between said relief valve and said source of pressurized fluid, said second valve having pilot connections at each of its two positions,

said second valve being biased to one of its two positions and operating to the other of its positions when P (A /Ag P P psi, where P fluid pressure in said second conduit (AJA area ratio between the two pilot connections of said second valve I P =fluid pressure on the side of said relief valve opposite to said second conduit, and

P arbitrary bias pressure (spring pressure).

2. Apparatus according to claim 1 in which said relief valve is piloted, the pilot area being approximately ten times the flow area.

3.'Apparatus according to claim 2, in which the condition for said relief valve opening is lOP -l-P P +P mi,where' P is the fluid pressure in said first conduit, and P is the relief valve setting.

LII

6. Apparatus according to claim 1, in which P (A,jA,) P; P psi when the load pressure is approximately 90 percent of said source pressure.

7. Apparatus according to claim 1 in which (A /Ad is selected so that said second valve will operate to its said other position at a minimum setting of said source pressure.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION P t n 3.667.227 Dated June 6,- 1972 Inventor-(s) JEROME BENTKOWSKY ET It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Colunm 2, line 25, capital "D" should be a capital C-.

Same column, between lines 18 and 19 insert P is the relief valve setting.--.

Same column, line 43', before "805 psi" insert -arbitrary bias pressure (spring pressure) of Signed and sealed this 17th day of April 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents F ORM PO-105O (10-69) USCOMM-DC 60376-F 69 U.S, GOVERNMENT PRINTING OFFICE: 1969 0-366-334 

1. Apparatus for limiting the load on the output of a hydraulic drive system to an essentially constant value regardless of whether the load is being driven or is overpowering the drive, said apparatus comprising: a source of pressurized fluid; a fixed displacement hydraulic motor; a load connected to said motor; a first control valve having a neutral position and two selectively settable positions; means responsive to the selective actuation of said first valve to one of its two settable positions to cause fluid to flow from said source through a first conduit to operate said motor in one direction of rotation; means responsive to the selective actuation of said first valve to the other of its two settable positions to cause fluid to flow from said source through a second conduit to operate said motor in the opposite direction of rotation; a relief valve in said second conduit; and a second two-position valve located between said relief valve and said source of pressurized fluid, said second valve having pilot connections at each of its two positions, said second valve being biased to one of its two positions and operating to the other of its positions when PD > OR = (A2/A1) PE + PT psi, where PD fluid pressure in said second conduit (A2/A1) area ratio between the two pilot connections of said second valve PE fluid pressure on the side of said relief valve opposite to said second conduit, and PT arbitrary bias pressure (spring pressure).
 2. Apparatus according to claim 1 in which said relief valve is piloted, the pilot area being approximately ten times the flow area.
 3. Apparatus according to claim 2, in which the condition for said relief valve opening is 10 PC + PD > or = PE + PR psi, where PC is the fluid pressure in said first conduit, and PR is the relief valve setting.
 4. Apparatus according to claim 3 in which application of an external load to said system will cause said second valve to operate to its said other position when the system return pressure reaches approximately 805 psi.
 5. Apparatus according to claim 4 in which said relief valve is arranged to open when PD PR thereby causing said drive system to slip.
 6. Apparatus according to claim 1, in which PD > or = (A2/A1) PE + PT psi when the load pressure is approximately 90 percent of said source pressure.
 7. Apparatus according to claim 1 in which (A2/A1) is selected so that said second valve will operate to its said other position at a minimum setting of said source pressure. 